Our major project is to complete a study of the dependence of AIB fluxes on the concentrations of sodium, potassium, and hydrogen ions in the extracellular medium of Ehrlich ascites tumor cells. A study of one-way fluxes in the steady state and at zero intracellular concentration has been completed. It has not been practical to examine one-way fluxes at a large number of concentrations of sodium and potassium. This is practical if net fluxes are measured and such a study has been started. Exploratory work to find an artificial thick lipid membrane that is rugged and has reproducible permeability characteristics has been completed. We are now characterizing the dependence of permeability of such membranes on their phospholipid composition. The ultimate goal is to use these in attempts to reconstitute transport systems in vitro.